1. Field of the Invention
The present invention relates to a numerical control apparatus for machine tool and a numerical control method for machine tool. Particularly it relates to a numerical control apparatus and method in which circumferential velocity can be controlled to be kept constant even in operation under electronic cam program control to thereby attain regulation of cutting velocity and improvement in machining accuracy and in which efficiency in transformation of an NC program into an electronic cam program can be improved to thereby attain improvement in machining efficiency.
2. Description of the Related Art
There is commonly known a numerical control machine tool used for machining a material into a desired shape by using a tool such as a cutter in the condition that the material is set in the machine tool. For example, the numerical control machine tool operates as follows. A numerical control program (NC program) is generated. Respective portions inclusive of the tool such as a cutter are operated automatically by the NC program to thereby obtain a product machined into a desired shape.
The NC program per se generated for obtaining such a machined product can be generally generated and corrected on the numerical control machine tool. When, for example, nonconformity that the machined product does not satisfy tolerance on design is detected as a result of trial cutting of the machined product, the NC program can be corrected on the machine tool side to eliminate the nonconformity. As result, high working efficiency can be provided.
On the other hand, use of an electronic cam program instead of the NC program is known. A material set in a machine tool is machined into a desired shape by use of a tool such as a cutter under control using the electronic cam program. For example, control using the electronic cam program has been disclosed in JP-A-2001-170843.
That is, as disclosed in JP-A-2001-170843, command data of a moving axis at every moment is generated on the basis of rotation position data generated at every moment by a pulse signal output from a pulse encoder mounted on a reference axis and command position data of the moving axis set in accordance with unit rotation position of the reference axis. Command velocity data of the moving axis in synchronism with the rotational velocity of a rotary object is generated on the basis of the moving command data and the rotation position data. The position of a tool is controlled on the basis of the moving command data and the command velocity data generated as described above. In the numerical control machine tool using this type electronic cam program, respective position data of a tool and a workpiece with respect to an accumulated rotation angle of a main shaft are decided. There is an advantage that machining can be made accurately in a short time compared with the numerical control machine tool using the NC program.
Generally, graphic information, designated machining paths, machining steps, tool information, tooling information, etc. are input to a CAM software or the like installed in a personal computer or the like provided separately from the numerical control machine tool to thereby generate this type electronic cam program. It is conceived that a certain kind of transformer software is used for transforming an NC program into an electronic cam program.